Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$116.77	10.209%	$128.691	$128.69	$128.70	$128.70
Purchase #2	$204.77	12.547%	$230.4625	$230.46	$230.45	$230.50
Purchase #3	$146.75	6.753%	$156.66	$156.66	$156.65	$156.70
Purchase #4	$227.56	12.461%	$255.9163	$255.92	$255.90	$255.90
Purchase #5	$164.30	9.589%	$180.0547	$180.05	$180.05	$180.10
Purchase #6	$81.83	8.606%	$88.8723	$88.87	$88.85	$88.90
Purchase #7	$237.57	9.235%	$259.5096	$259.51	$259.50	$259.50
7 purchase totals =	$1,179.55		$1,300.1664	$1,300.16	$1,300.10	$1,300.30